Filament regulator circuit



1 1956 E. A. ANDRADE FILAMENT REGULATOR CIRCUIT Filed April 10, 1953 aw k Wm m+ ll IWAII m u I M w. \v Q h QUFQJDQU INVENTOR. EDWARD A. ANDRADE 5, ATTORNEY United States Patent 2,775,734 FILAMENT REGULATOR CIRCUIT Edward A. Andrade, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application April 10, 1953, Serial No. 348,004 3 Claims. (Cl. 323-45) This invention relates in general to electronic alternating current voltage regulators and in particular to a voltage regulator which operates with a saturated tube.

Since power is proportional to the root-mean-square of an alternating voltage rather than to its peak value oraverage value, it is oftentimes particularly desirable that an alternating voltage be regulated by its root-mean square value rather than its peak or average value. Rootmean-square voltage regulation is particularly useful when furnishing a voltage for the filaments. of vacuum tubes. A filament requires constant power to maintain a constant temperature and variations in peak or average voltages are immaterial as long as the power remains con stant.

An example of an alternating voltage regulator which regulates by average voltage value rather than rootmean-square voltage value is a circuit which rectifies a sample output and regulates the alternating output to maintain the rectified sample at a constant voltage. It is therefore the principal object of this invention to pro vide a voltage which is regulated so as to obtain a constant root-mean-square value.

Both alternating and direct current voltage sources have been used at various times to heat tube filaments. oftentimes in direct current systems there is no available separate source for the low voltage that is ordinarily required for filament heating. Therefore a large dropping resistor is required which causes large power losses and thereby inefficient power distribution.

Alternating current may be used more efficiently for filament heating because a low voltage may be obtained by transformation without the power dissipation that is unavoidable in a direct current circuit. It is therefore another object of this invention to provide a filament heating circuit which operates at high efficiency.

This invention comprises a regulator which has a diode that has its filament connected across the circuit output. The diode, which is operated at saturation, produces a plate current that is proportional to the root-mean-square of the output voltage. The diodes plate current controls the bias for the grid of a triode which acts as a variable resistor in a phase shift circuit. The phase shift circuit controls the current output of a pair of thyratrons operated in push-pull. The thyratron output is transformed by an output transformer to furnish the desired regulated voltage.

Other objects, features and advantages of this invention will become apparent to those skilled in the art from the following specification and drawings, in which:

Figure 1 is a schematic diagram of this invention; and

Figure 2 shows the vector relationships among various currents and voltages in the circuit.

Now referring to the invention in more detail, Figure 1 shows an input transformer T1 which has a primary and a secondary 11 with a grounded center tap 12 which divides secondary 11 into two equal parts 13 and 14. A first coil 16 of an output transformer T2 has one side connected to part 13 and its other side connected to the plate 17 of a thyratron tube V1. A second coil 18 of transformer T2 has one end connected to part 14 and its other end connected to the plate 19 of a second thyratron tube V2.

A control transformer T3 has a secondary 22 with a grounded center tap 23 which divides it into equal parts 2,775,734 Patented Dec. 25, 1956 24 and 26. Part 24 is connected to the control grid 31 of Tube V1 and part 26 is connected to control grid 32 of tube V2. The cathodes 33 and 34 of thyratrons V1 and V2 are grounded.

One side of the primary 27 of transformer T3 is connected to the plate 36 of a triode V3 and its other side is connected to a B plus power supply, and to a cathode 37 of tube V3 through resistor R1. Cathode 37 is connected to ground through a biasing resistor R2. A capacitor C1 is connected between plate 36 of tube V3 and part 14 of transformer T1 by lead 35.

The grid 38 of tube V3 is connected to the plate 41 of a diode connect-ed pentode V4. A load resistor R4 is connected between plate 41 and a B plus supply, and a grounded filament 42 is connected across the circuit output terminals 29 and 30 through a limiting resistor R5 and a potentiometer Rs with a tap 39.

The basis for operation of this invention is the sensitivity of plate current of a saturated diode to changes in filament heating power. This sensitivity is used to control the output of a thyratron circuit which then pro duces a constant root-mean-square alternating voltage. The saturated condition of the diode prevents variations in B plus voltage from afiecting the current output of the diode which thereby makes it sensitive only to changes in filament power.

To operate the circuit, an alternating current power source, which might be a volt alternating current source, is connected across primary 10 of transformer T1 to terminals 15 and 20. This induces equal and opposite voltages E1 and E2 in secondary parts 13 and 14 which furnish the plate voltages for thyratrons V1 and V2, respectively. Voltage E2 also appears across the circuit consisting of capacitor C1, and tube V3 in parallel with primary 27 and resistor R1, and grounded resistor R2.

Voltage E2 will cause an alternating current i to flow through capacitor C1 which will divide into a larger part I1 which flows through tube Va and a much smaller part I2 which flows through primary 27. The tube V3 appears as a substantially resistive impedance to current I1. Primary 27 furnishes a substantially resistive impedance to current 12 because the plate resistance of V3 is lower than the reactance of primary 27. Therefore currents I, I1 and I2 will all be substantially in phase as shown in Figure 2.

The voltage EC across capacitor C1 will lag current I by substantially ninety degrees, and the voltage Eb across resistor R2 will be in phase with current I. Since the tube V3 is essentially a resistance, the voltage Ep across tube V3 will be in phase with current I1 and will also be in phase with currents I and I2. The vectorial sum of voltages Eb, Ep and E0 is E2 which is shown vectorially in Figure 2.

As current 12 passes through primary 27, it induces equal and opposite voltages E3 and E4 in the respective secondary parts 24 and 26 of control transformer T3 which are in quadrature with current 12 and thereby are in quadrature with voltages Ep and Ba. The voltage E4 is the control grid voltage for thyratron V2 and it will lag the voltage E2 which is the plate voltage of the thyratron V2, by the phase angle 2. Likewise, the voltage E3, which has the opposite phase of voltage E4, is the control grid voltage for thyratron V1. It will lag plate voltage E1 which is opposite in phase from voltage E2, by an angle 1, and that must be equal to the angle 2, as will be seen in Figure 2.

The plate resistance of tube Va will vary with its grid bias voltage Ed. The grid Voltage Ea which is the plate voltage of tube V4 will, in turn, change with the plate current of saturated diode V4. The output current of a saturated diode is primarily a function of the power absorbed by its filament which in turn is a function of the roct-mean-square filament voltage Er. The output voltage E1 of diode V; will then be a function of the root-mean-square voltage Er across filament 42, and since voltage Er proportionally varies with the rootmeans-square output voltage E across terminals 29 and 30, the bias voltage Ea must then vary with the rootmean-square voltage E0. When the voltage Ed changes, the plate resistance of tube V3 correspondingly changes to vary the relative lengths of the vectors EC, Ep and Eb in Figure 2 which cause the phase angles or and 2 to alter the thyratron output in such direction as to oppose the initial change in voltage E0 to maintain it constant.

The resistor R5 and potentiometer Re are merely used to limit the current through the filament 42 so it will operate in its saturated state, but they do not disturb the proportionality between root-mean-square output voltage E0 and filament voltage Er. A small directly heated pentode connected as a diode has been used for tube V4 to minimize the time constant of the regulator. The directly heated filament type of tube will follow changes more rapidly than the cathode type. It is to be understood that any type of tube operated as a diode may be substituted for the pentode shown.

For example, suppose the output voltage E0 increases, then filament 42 will become hotter thus causing an increased current to flow through tube V4. Since tube V4 and resistor R4 are connected in series between ground and B plus, an increase in current will cause the voltage of plate 41 to decrease. This decreases the bias on grid 38 of tube V 3 which results in a phase shift in the thyratron control circuits so as to decrease E0. Thus, E0 will remain constant. A similar effect is observed when E0 becomes smaller and it will be increased to the desired value by the action of the circuit.

It is then seen that the plate currents of thyratrons V1 and V2 will be regulated according to the root-mean-square output voltage E0 of the circuit. Since the thyratrons provide the current through primary coils 16 and 18 which induce the output voltage in the secondary 21 of output transformer T2, the regulation of the output voltage is obtained by regulating the thyratron plate current. The constant value of output voltage E0 which is induced in secondary 21, can be made any desired value by suitable choice of turns ratio and by adjusting contact 39.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention, as defined by the appended claims.

I claim:

1. Means for regulating an output voltage comprising, an output terminal, an output transformer with its secondary connected between ground and the output terminal, a pair of primaries of said output transformer, a pair of thyratron control tubes with cathodes connected to ground, the primaries of said output transformer connected on one side of to the plates of said thyratrons respectively, an input transformer with its primary connected to an alternating input voltage, the center tap of the secondary of said input transformer connected to ground, one end of the secondary of said input transformer connected to the other side of one of the primaries of said output transformer, the other end of the secondary of the input transformer connected to the other side of the second primary of the output transformer, a control transformer with the midpoint of its secondary connected to ground and opposite ends thereofconnected to control grids of the first and second thyratron tubes, a phase shift circuit comprising a condenser and triode tube operating as a variable resistor connected in series between one end of the secondary of the input transformer and ground, the primary of the control transformer connected in the plate circuit of said triode tube, a B plus voltage connected to said control primary, a resistor connected in series with said B plus voltage, a pentode connected as a diode connected between said resistor and ground, the plate of said pentode connected diode tube connected to the control grid of said triode tube, a potentiometer connected to the output terminal, and an output from said potentiometer supplied to the filament of said pentode connected diode tube to operate it in a saturated state.

2. Means for regulating the power of an alternating output voltage comprising, a pair of thyratron control tubes with their cathodes connected to ground, an input transformer with its primary connected to an alternating input voltage, a center tap of the secondary of said input transformer connected to ground, an output transformer with a pair of primaries connected on one of their sides to the respective plates of the thyratron control tubes and connected on their other sides to the ends of the input secondary, a pair of output terminals, the secondary of said output transformer connected between the output terminals, a vacuum tube connected as a diode with its filament connected serially to said output voltage, a direct plate voltage supply, a resistor connected between the plate of said diode and said plate voltage supply, said plate voltage adjusted to saturate said diode, a phase shift circuit comprising a condenser and a triode tube and a cathode resistor connected serially between one side of said input secondary and ground, the grid of said triode tube connected to the plate of said diode, a control transformer, a circuit comprising a resistor and said control transformer primary connected serially between the plate and cathode and cathode of said triode tube, the plate voltage supply connected in the plate circuit of said triode, the ends of the control transformer secondary connected to the control grids of said thyratron tubes, and the center tap of the control transformer secondary connected to ground.

3. Means for regulating the power of an alternating output voltage comprising, an input transformer with its primary connected to an alternating input voltage, the midpoint of the secondary of said input transformer connected to ground, an output transformer with a pair of primaries and a secondary, a pair of gas control tubes with grounded cathodes and screen grids, the plates of said gas tubes connected to opposite ends of the pair of primaries of said output transformer, the other ends of said pair of primaries connected to the respective ends of said input secondary, the secondary of said output transformer connected between an output terminal and ground, a vacuum tube connected as a diode operating in a saturated condition with its filament connected serially across the output terminals, a first resistor connected in series with the plate of said diode connected tube and to a B plus plate voltage source, a phase shift circuit comprising a condenser and a second vacuum tube with at least one grid connected serially between ground and one side of said input secondary, the control grid of said second vacuum tube connected to the plate of said diode connected tube, a control transformer with one side of its primary connected to the plate of said vacuum tube and the other side of the primary connected to the B plus supply voltage, a resistor connected between the other end of said control primary and the cathode of said second vacuum tube, the center tap of the secondary of said control transformer connected to ground, and the opposite ends of the secondary or" said control transformer connected to the control grids of the first and second gas tubes.

References Cited in the file of this patent UNITED STATES PATENTS 1,914,193 Bedford June 13, 1933 1,947,197 Gorman Feb. 13, 1934 2,392,434 Trucksess Jan. 8, 1946 2,444,472 Schooley July 6, 1948 

